A fascia (plural: fasciae) is primarily a collagenous connective tissue fiber that forms sheets or bands beneath the skin to attach, stabilize, enclose, and separate muscles and other internal organs. Fasciae are very similar to ligaments, aponeuroses, and tendons as they are all made up of collagen fibers; however, ligaments join bones together, tendons join muscles to bone, but fasciae wrap around muscles or other structures like fat – superficial fasciae.
Fasciae can be classified into:
- Superficial fascia (also called subcutaneous tissue)
- Deep fascia (muscle fascia)
- Visceral (or parietal) fascia
Functionally, fasciae reduce friction between muscles, allowing sliding, suspend organs within their cavities, transmit movement from muscle to bones, support and provide movable wrapping for nerves and blood vessels as they pass through and between muscles. However, for fascia lata, its primary function is to reduce friction between muscles, hence it is a deep fascia.
The fascia lata encloses the muscles and forms the outer limit of the fascial compartments of thigh, that is, it limits the outward expansion of contracting muscles, making muscular contraction more efficient in compressing veins to push blood towards the heart. Although the fascia lata encloses the thigh muscles and form the outer limits, it is internally separated by intermuscular septa.
The fascia lata is an investment for the whole thigh. It is substantial because it encloses the large thigh muscles, especially laterally, where it is thickened and strengthened by additional reinforcing longitudinal fibers to form the iliotibial tract (a structure that runs to the tibia and serves as a site of muscle attachment).
That broadband of fibres (iliotibial tract) is the shared aponeurosis of the tensor fasciae latae and gluteus maximus muscles. The iliotibial tract extends from the iliac tubercle to the anterolateral tubercle of the tibia (also called the Gerdy tubercle).
The fascia lata and fascial intermuscular septa (three fascial intermuscular septa) form the walls of the muscular compartments of the thigh, and separate the thigh muscles into three compartments. The compartments are:
- The anterior compartment
- The medial compartment
- The posterior compartment
The three intermuscular septa arise from the deep aspect of the fascia lata and attach to the linea aspera of the femur (thigh bone). The lateral intermuscular septum (one of the three fascial intermuscular septa) is very strong, while the other two are relatively weak. This lateral intermuscular septum is of clinical importance as it offers an internervous plane (plane between nerves) to surgeons needing wide exposure of the femur. This septum extends deeply from the iliotibial tract to the lateral lip of the linea aspera and lateral supracondylar line of the femur.
The fascia lata is especially marked by an important opening or hiatus called the saphenous opening. The great saphenous vein traverses the fascia lata through that opening. The saphenous opening in the fascia lata is approximately 3.75 cm in length and 2.5 cm in breadth, and its long axis is vertical. Its (saphenous opening) medial margin is smooth but its superior, lateral and inferior margins form a sharp crescentic edge, the falciform margin. The saphenous opening is inferior to the medial part of the inguinal ligament, approximately 4 cm inferolateral to the pubic tubercle.
The fascia lata attaches and is continuous with:
- The inguinal ligament, pubic arch, body of pubis, and pubic tubercle – anteriorly
- The membranous layer of subcutaneous tissue or superficial fascia (Scarpa fascia) of the inferior abdominal wall
- The iliac crest – laterally and posteriorly
- The sacrum, coccyx, sacrotuberous ligament, and ischial tuberosity/ischiopubic ramus (branch) – posteriorly and medially
The inferior attachments and continuations of the fascia lata are as follows:
- The fascia lata is attached to the exposed parts of bones around the knee – the condyles of the femur and tibia, the head of the fibula, and the sides of the patella (the attachment to the patella is strengthened by transverse fibres from the lower parts of the Vasti, which are attached to- and support the patella)
- The fascia lata is also attached to the deep fascia of the leg, inferior to the knee joint. This deep fascia of leg is called the crural fascia (crural is derived from the Latin word crus, meaning leg). The crural fascia is a continuation of the fascia lata.
Deep fasciae are very sensitive, and as a general rule, its nerve supply is that of the overlying skin. Hence, the terminal branches of some of the nerves innervating the thigh, especially those running to the skin of the thigh and pelvic regions, also innervate the fascia lata. The fascia lata is innervated by:
- Ilioinguinal nerve
- Femoral branch of the genitofemoral nerve
- Medial, intermediate and lateral femoral cutaneous nerves
- Cutaneous branch of the obturator nerve
All of those nerves also pierce the fascia lata to supply the overlying skin. For example, the cutaneous branch of the obturator nerve supplies the area of skin above the medial side of the knee after piercing and innervating the fascia lata.
The fascia lata is pierced by:
- The superficial iliac circumflex artery
- The superficial epigastric artery
The superficial external pudendal artery traverses the saphenous opening of fascia lata.
The venous return of the fascia lata include the perforating veins (accompanying the superficial circumflex iliac artery, superficial epigastric artery, and superficial and deep external pudendal arteries) of the great or long saphenous vein. Accompanying veins like these are referred to in Latin as venae comitantes. The great saphenous vein is the longest vein in the body, traversing the saphenous opening of the fascia lata. It is one of the most important veins in the body in view of the prevalence of varicosities (abnormal swellings or dilations) developing at its lower end.
The lymphatic drainage of the fascia lata is by lymph vessels which empty into the vertical group (one of the three groups of lymph nodes of the lower limb) of lymph nodes lying lateral to the termination of the long saphenous vein.
The fascia lata has been reported to be a major source of fascia used for reconstruction surgery, for example in the management of ptosis of the upper eyelid.
Trauma to muscles and/or vessels in the compartments of the thigh or leg can lead to compartment syndromes characterized by hemorrhage, edema, and inflammation of the muscles.
As the fascial compartments of the lower limbs are generally closed spaces, ending proximally and distally at joints, and the deep fascia (fascia lata or crural fascia) and septa forming the boundaries (external limits of the fascia compartments) are strong, the increased volume, consequent to the trauma, increases the intracompartmental pressure.
Thus, Fasciotomy is usually performed to relieve the pressure in the compartment(s) concerned. A Fasciotomy is simply the incision of an overlying fascia or septum, usually to relieve the pressure in a fascial compartment.